1. Field of the Invention
The present invention relates generally to a method for performing handoff in a wireless communication system and a system thereof, and more particularly, to a method capable of performing handoff between heterogeneous networks and a system thereof.
2. Description of the Related Art
Generally, wireless communication systems have been developed for situations when it is not possible to connect a fixed wired network up to a terminal. With progress in communication technology, wireless communication systems have developed into mobile communication systems. The 4th generation mobile communication system supports ultrahigh-speed multimedia service beyond the 1st generation analog system, the 2nd generation digital system, and the 3rd generation IMT-2000 system supporting the high-speed multimedia service. The IMT-2000 system is roughly classified into the asynchronous system and the synchronous system. Typical asynchronous systems include the Universal Mobile Telecommunication Systems (UMTS) and Wideband Code Division Multiple Access (W-CDMA) systems proposed by 3rd Generation Partnership Project (3GPP), and typical synchronous systems include the CDMA 2000 1x, CDMA 2000 1x Evolution Data Only (EV-DO), and CDMA 2000 1x Evolution of Data and Voice (EV-DV) systems proposed by 3rd Generation Partnership Project 2 (3GPP2).
A typical example of the 4th generation mobile communication system can include the Worldwide Interoperability for Microwave Access (WiMax) system proposed by Institute of Electrical and Electronics Engineers (IEEE). The WiMax system is defined as the IEEE 802.16e standard for providing Wireless Broadband Internet (WiBro) service to mobile terminals, and is now in the preparation phase for commercialization. The WiMax system allows the mobile terminal to wirelessly provide various multimedia services such as Internet access service, high-speed data service, image service, etc. as well as the voice service regardless of the time and place, whether it is on the move or at a standstill. Therefore, the WiMax system attracts public attention as the mobile communication technology capable of meeting the highly-increasing user demand for the wireless Internet service.
In this way, several different types of communication networks coexist in the current mobile communication system. In addition, due to the development of the mobile communication technology and the increase in the number of available wireless services, users carrying mobile terminals are increasing in number, causing an increase in the interest in the mobile terminal-based services. Thus, a handoff method between heterogeneous networks is necessary for providing better communication services. The term ‘handoff’ as used herein refers to a technology allowing a user to seamlessly maintain the communication service while moving from the coverage of one base station (or access network) to the coverage of another base station.
A handoff method between homogeneous networks is now available in the WiMax system. However, not many handoff methods between heterogeneous networks have been proposed in detail. In particular, there is no detailed scheme proposed for the handoff method between the WiMax system and the EV-DO system. Therefore, there is a demand for an efficient scheme for the handoff method between the WiMax system and the EV-DO system, among the handoff methods between heterogeneous networks.
FIG. 1 is a diagram illustrating the architecture of a general 1xEV-DO network (DO network). The DO network includes a Packet Data Service Node (PDSN) 101, connected to the Internet 100, for transmitting high-speed packet data to Access Networks (ANs) 103, and Packet Control Functions (PCFs) 102 for controlling the ANs 103. Each of the ANs 103 wirelessly communicates with a plurality of terminals (commonly known as Access Terminals (ATs)) 104, and transmits the high-speed packet data to the terminal having the highest data rate.
FIG. 2 is a diagram illustrating the architecture of a general WiMax network. The WiMax network includes Base Stations (BSs) 202, each of which wirelessly communicates with a plurality of terminals (commonly known as Mobile Stations (MSs)) 203 and provides the ultrahigh-speed multimedia service, and an Access Service Network (ASN) 201, connected to the Internet 200, for transmitting high-speed packet data to the BSs 202.
Due to the development of the mobile communication industry and the increase in the user demand for Internet services, there is an increasing demand for the mobile communication system capable of efficiently providing Internet services. The conventional mobile communication network, as it was developed to mainly provide the voice services, has the narrower data transmission bandwidth and the higher service charge. IEEE 802.16 Standard Group, one of International Standard Groups, proposes the IEEE 802.16e standard as a standard for providing the WiBro service for mobile terminals.
The typical example of the IEEE 802.16e-based wireless communication system can include a WiMax (also known as WiBro) system. As for the handoff method in the WiMax system, there are handoff technologies proposed for the conventional CDMA 2000 1x system and EV-DO network, but there is no efficient handoff method between heterogeneous networks, designed taking into account the characteristics of the heterogeneous networks. Due to the development of the mobile communication technology and the increase in the number of available wireless services, users carrying mobile terminals are increasing in number, causing an exponential increase in the interest in the mobile terminal-based services. In order to manage locations of the mobile terminals and allow the mobile terminals to provide seamless communication services even during handoff, each mobile communication system proposes a handoff technology suitable for the corresponding mobile communication system. However, many efforts to provide the handoff technology have been chiefly made to efficiently support intra-network handoff, for example, handoff within the 3GPP2 network or the WiMax network.
When the characteristics of the current communication system where heterogeneous networks coexist are taken into consideration, a handoff method between heterogeneous networks is indispensable. For the evolved next generation network, rev C is now prepared in the 3GPP2 EV-DO network, and one of the matters to be dealt with in rev C is the handoff technology between 3GPP2 rev C and rev A. Further, there is no detailed scheme proposed for the handoff method between the EV-DO network and the WiMax network, commercialization of which is now in preparation after completion of its standardization. Therefore, there is a demand for an efficient scheme for a handoff method between the WiMax system and the EV-DO network, among the handoff methods between heterogeneous networks.